The present invention relates to reactive hotmelt adhesive compositions having adhesive characteristics in respect of both reactivity (curability through reaction) and hotmelt applicability.
Reactive hotmelt adhesive compositions are already known which comprise a urethane prepolymer having an isocyanate group at each end and obtained by the reaction of polypropylene glycol or like polyether diol with tolylene diisocyanate or like diisocyanate, and rosin ester resin, coumarone-indene resin or terpene phenolic resin which is substantially not reactive but compatible with the urethane prepolymer and admixed as a tackifier with the prepolymer (see, for example, Unexamined Japanese Patent Publication SHO 61-115977 and Examined Japanese Patent Publication SHO 51-30898).
However, the urethane prepolymer obtained by reacting a diisocyanate with a polyether diol is poor in compatibility with various tackifiers and is therefore usable only with specified tackifiers like those mentioned above. Accordingly, the adhesive compositions still remain to be improved in properties.
For example, the adhesive composition containing rosin ester resin is insufficient in heat resistance, whereas the one incorporating coumarone-indene resin gives off a strong offensive odor. The adhesive composition comprising terpene phenol resin is unsatisfactory in storage stability. Moreover, any of these adhesive compositions is insufficient in weather resistance. These compositions further require a relatively long period of time to obtain useful bond strength, hence a low reaction velocity, and they have yet to improved in this respect.